This invention relates to an image information processing system in which recording or displaying changes depending on the display or record characteristics of the display destination as in a workstation, etc., connected to a network to which facsimile machines and printers are connected, and in particular to an image information processing system which enables good images to be displayed or recorded independently of such display or record characteristics.
If an image information processing system for recording monochrome binary image data, typified by a facsimile machine, binarizes read image information simply, it cannot reproduce a delicate tone of a halftone image such as a photograph although it can reproduce good line drawings. Then, hitherto, false halftone processing of artificially reproducing halftone, such as a dithering method or an error diffusion method, has been adopted if such an image information processing system needs to reproduce halftone. In the false halftone processing, light and shade are produced according to the occupation percentage of black pixels in a unit area; this is referred to as area gradation representation.
FIG. 16 represents the density of each unit pixel of an original document at 256 levels. An arrow 101 indicates a horizontal scanning direction as a placement direction of an image sensor (not shown) for an original document 102 and an arrow 103 orthogonal to the direction indicates a vertical scanning direction. The unit pixels correspond to record elements in the minimum units for display (the term "display" simply mentioned in the specification contains recording by a recorder as well as displaying on a display, but only recording by the recorder will be hereinafter referred to as record(ing) in principle.)
FIG. 17 represents one example of threshold values of a dither matrix. In the example, the dither matrix 110 has an 8.times.8 matrix structure in which 64 threshold values are set in total.
FIG. 18 represents a part of image data resulting from binarizing the image information of the maniscript shown in FIG. 16 using the dither matrix shown in FIG. 17. The image data 120 corresponds to data provided by putting the dither matrix 110 shown in FIG. 17 on the 8.times.8 unit pixel area in the upper left corner of the original document 102 in FIG. 16 and binarizing the densities of the unit pixels with the corresponding threshold values in the dither matrix 110. For example, for the unit pixel in the upper left corner, the image information density 67 and the threshold value in the dither matrix 110 corresponding thereto is 0, thus the unit pixel is converted into a black unit pixel 121. For the unit pixel 122 horizontally adjacent to the unit pixel 121, the image information density is 71 and the threshold value in the dither matrix 110 corresponding thereto is 128, thus the unit pixel is converted into white. Other pixel units are processed in a similar manner.
FIG. 19 shows an example of an error diffusion process pattern. In the error diffusion process pattern 130 in the figure, the unit pixel indicated by X is the current unit pixel 131 to be processed. The threshold density level is 128, a half of 256 gradations.
FIG. 20 represents a part of image data resulting from binarizing the image information of the original document shown in FIG. 16 using the error diffusion process pattern shown in FIG. 19. In the error diffusion technique, the current unit pixel 131 scans starting at the upper left corner of the original document 102 (FIG. 16) in order and binarization is performed to generate image data 140. First, for the unit pixel 141 in the upper left corner of the original document 102 shown in FIG. 16, binarization of density 67 with threshold value 128 is executed, resulting in a white pixel.
Since the density of the white pixel is 0 at the recording time, an error corresponding to density 67 occurs. Then, the error is distributed to the pixel units in the process pattern 130. At a 1/8 distribution place, 8.4 density occurs and at a 3/8 distribution place adjacent to the 1/8 distribution place, a 25.1 density error occurs. Likewise, the process pattern 130 moves on the original document 102 in such a manner that the respective unit pixels are scanned for each line in order, and binarization processing of the pixel units is performed. In the error diffusion technique, binarization is executed while occurring errors are added, thus finally no density error occurs.
By the way, FIGS. 18 and 20 assume that the black or white pixels in image data 120, 140 are rectangles of the same size and are placed with no gaps. However, the size of each unit pixel at the recording time varies from one recorder to another because of the recording system difference, etc., under the present circumstances.
FIGS. 21 and 22 illustrate how image data provided by false halftone processing as shown in FIG. 18 or 20 is recorded by a recorder in different densities. In the example shown in FIG. 21, the size of a record dot 151 indicated by a black dot (.circle-solid.) is smaller than that of a unit pixel, in which case the black occupation area when area gradation representation is applied decreases relatively, thus the image is represented as a low-density image as a whole. In the example shown in FIG. 21, the black dot occupation percentage is about 17% and corresponds to the gradation of the eleventh level in 64 levels.
In contrast, in the example shown in FIG. 22, the size of a record dot 161 is larger than that of a unit pixel, in which case the black occupation area when area gradation representation is applied increases relatively, thus the image is represented as a high-density image as a whole. In the example shown in FIG. 22, the black occupation percentage becomes about 38% and corresponds to the gradation of the 24th level in 64 levels. Generally, laser printers tend to provide larger black dot diameters as shown in FIG. 22.
Even if the image data is subjected to the same false halftone process, if it is recorded by different recorders, it is represented at different densities; the image of the image data recorded by one recorder is represented almost in white and the image of the same image data recorded by another recorder is represented almost in black.
When the copy function of a facsimile machine is positively used or reading and recording of an image is performed by a single machine like a copier, of course, adjustments of threshold values in a dither pattern, for example, as shown in FIG. 17 can be carried out individually in response to the record characteristics of the recorder of the machine. Therefore, if such an image information processing apparatus comprises a recorder wherein there is a fear that the density may become low as a whole as shown in FIG. 21, for example, the threshold values are preset low, whereby the threshold level at binarization can be lowered and the whole density level can be enhanced. In contrast, if the image information processing system comprises a recorder wherein there is a fear that the density may become high as a whole as shown in FIG. 22, for example, the threshold values are preset high, whereby the threshold level at binarization can be raised and the whole density level can also be lowered.
However, for example, a present apparatus may read image information and send it to a recorder of another apparatus for recording the image information. Typically, image information read by one facsimile machine is sent to another facsimile machine for reproducing an image. In such a case, if compatibility between the two machines is poor, the image information reproduced by the receiving image information processing apparatus may become considerably dark or pale.
For example, the present apparatus may record with comparatively small record dots as shown in FIG. 21. In such a case, the present apparatus lowers the threshold level and intentionally increases the black area occupation percentage so that the density of the original document 102 as shown in FIG. 16 is reproduced intact. However, when the apparatus thus changing the threshold level and binarizing data sends the resultant image data to another image information processing apparatus, if the recorder of the receiving image information processing apparatus has a record characteristic as shown in FIG. 22, the image data processed darkly is recorded furthermore darkly.
In contrast, it is assumed that there is an image information processing apparatus comprising a recorder having a record characteristic as shown in FIG. 22. This image information processing apparatus reads an original document 102, processes an image slightly palely, and records the resultant image by a recorder of the apparatus, thereby adjusting the image density. However, assuming that image data prepared by such an image information processing apparatus is binarized and then the resultant data is sent to a recorder having a record characteristic as shown in FIG. 21, the image data processed somewhat palely in dithering is used to perform image reproduction processing palely more and more, thus the image is represented excessively palely.
In any case, the number of gradations of an image that can be reproduced is decreased and the image quality is degraded. For example, if optimization is executed in the recorder having the record characteristic as shown in FIG. 21, about 24 black record dots are required to output the 16th gradation. When image data in the state is transmitted to the recorder having the record characteristic shown in FIG. 22, the 36th gradation is recorded and a low density cannot be reproduced.